1. Field
Embodiments of the present invention relate generally to gas turbine engines, and in particular, to a transition duct arrangement in a gas turbine engine and method installation thereof.
2. Description of the Related Art
A conventional gas turbine engine includes a compressor section, a combustion section including a plurality of combustors, and a turbine section. Ambient air is compressed in the compressor section and conveyed to the combustors in the combustion section. The combustors combine the compressed air with a fuel and ignite the mixture creating combustion products defining hot working gases that flow in a turbulent manner and at a high velocity. The working gases are routed to the turbine section via a plurality of transition ducts. Within the turbine section are rows of stationary vane assemblies and rotating blade assemblies. The rotating blade assemblies are coupled to a turbine rotor. As the working gases expand through the turbine section, the working gases cause the blades assemblies, and therefore the turbine rotor, to rotate. The turbine rotor may be linked to an electric generator, wherein the rotation of the turbine rotor can be used to produce electricity in the generator. The transition ducts are positioned adjacent to the combustors and route the working gases from the combustors into the turbine section through turbine inlet structure associated with a first row stationary vane assembly.
In engines with can combustors, such as in non-aero-derivative industrial gas turbine engines, the combustor is mounted at an angle to the main engine axis. Often this angle is selected based on previous design efforts which have an emphasis on easy-access to the fuel nozzles and combustion can for overhaul purposes. As a result, the transition duct not only has to transition the hot gas flow from the circular can combustor to a curved rectilinear inlet leading to the stationary vanes, but must also turn the flow from the axis of the combustor to the axis of the engine. This “bent-and-squished-tube” geometry results in localized hot spots leading to circumferential non-uniformity along the transition duct.
In order to maintain the metal temperature of the transition duct at a level below the oxidation limits of the bond coat, additional cooling air may be placed at the hotspot locations, typically leading to uneven heating of the transition duct and an increase in thermal stresses. Furthermore, the shape of the transition duct requires both axial and radial manipulation during the last few inches of assembly to align the transition duct with the first row of stationary vanes and to engage the transition mouth seals.
In one known technique, a non-uniform pattern of convective cooling channels, running from the inner diameter to the outer diameter of the transition duct, are placed on the upper and lower panels of the transition duct. Localized cooling is added where needed by using effusion cooling, typically near the side walls upstream of the exit face and under the aft support of the transition duct. The flow-path within the transition duct is coated with TBC (thermal barrier coating) to insulate the metal from the hot gas. The transition duct typically has a shorter service life than the turbine components do to the life limitations of the TBC.